The need for high performance, high capacity information technology systems is driven by several factors. In many industries, critical information technology applications require outstanding levels of service. At the same time, the world is experiencing an information explosion as more and more users demand timely access to a huge and steadily growing mass of data including high quality multimedia content. The users also demand that information technology solutions protect data and perform under harsh conditions with minimal data loss. And computing systems of all types are not only accommodating more data but are also becoming more and more interconnected, raising the amounts of data exchanged at a geometric rate.
Thus, today's data storage systems are used in computing environments for generating and storing large amounts of critical data. Some storage systems support many (e.g., hundreds) of disk drives. A hard disk drive is typically a device including a magnetic head, a motor, and one or more platters that store information. The motor turns a platter underneath the magnetic head.
The platter contains electrically encoded data that is detected by the magnetic head as the head passes over the platter. The platter can be read from or written to and is generally used to store data that will be accessed by the system. The hard disk drive is typically referred to as random access memory and is familiar to those skilled in the art.
Typically, data is arranged in concentric circles on the platter. The magnetic head is moved along a radius of the platter, and the magnetic head reader/writer accesses particular locations within the platter as the platter spins under the magnetic head. Those skilled in the art are familiar with the read and write operations of hard disk drives.
Constantly spinning the platter in the hard disk drive consumes a large amount of power. Specifically, a motor must be devoted to spinning the platter to allow access to the full physical array of data on the platter.
Powering a mechanical device, such as a motor, consumes a significant amount of power relative to the power consumed by the electronic circuitry within the system.
The consumption of electrical power is a major concern in many environments. For example, in data centers, computing equipment such as storage systems cause power consumption not only directly but also indirectly, because cooling equipment such as air conditioners are required to remove the heat given off by the computing equipment (and in at least some cases, since cooling equipment is not 100% efficient, the indirect consumption exceeds the direct consumption). In another example, power consumption is a major factor in the design and construction of portable computers. At least some of the concern over power consumption relating to portable computers arises due to their reliance upon batteries with a short life, e.g., batteries with a short life due to limited energy storage capacity.
In a typical practical implementation, a disk drive may consist of circuit board logic and a Head and Disc Assembly (HDA). The HDA portion of the disk drive includes the spindles platters, head arm and motor that make up the mechanical portion of the disk drive. When power is applied to the disk drive, the circuit board logic powers up and the HDA spins up. During spin up, the HDA requires a higher current than when it is in steady state, i.e., already spun up. This higher current is typically more than two times the steady state current. Therefore, if a storage system attempts to spin up many drives in the system at the same time, the system is required to support a peak power level that is much greater than the maximum power required to operate at steady state.
The more disk drives the system supports, the greater the peak power requirement. It is too expensive to provide a power subsystem that can support enough peak power to spin up many disk drives at once, especially when the excess power is not otherwise needed.
Some types of disk drives offer a separate HDA power input but no built in control over the timing of the application of power to the HDA. Some other types offer limited control. For example, Fibre Channel (“FC”) disk drives compliant with the SFF-8045 rev. 4.7 standard (“SFF-8045” or “8045”) allow the timing of HDA spin up to be controlled via two signal pins, Start_1 and Start_2, that allow the HDA to spin up based on three different conditions. Depending on the state of the Start_1 and Start_2 signals, the disk drive HDA will start drawing current either 1) immediately; 2) after it receives its first SCSI command, or 3) based on its arbitrated loop physical address (ALPA). This provides limited means to stagger the timing of spin up amongst all the drives such that system peak power requirements can be minimized. However, it is difficult for system software to use SCSI commands to control drive spin up timing, because insert and power control signals from the drives are asserted much faster than software can respond. (Under SCSI command mode, the drive is spun up by the controller issuing the command by the same process as data transfer commands are issued. In some interfaces, such as the ATA interface in at least some implementations, command mode is the only protocol available for drive power state management (i.e., there are no start bits).)
The ALPA address method is also disadvantageous in at least some circumstances. Consider a storage system capable of supporting 48 disk drives. If a user plugs a single disk drive into the 48th slot in a system in which the other drives are all already at steady state, there is no power-related reason why the drive should not spin up immediately. But because its spin up timing depends on its ALPA address, it will nonetheless take several minutes to spin up.
SFF-8045 describes a POWER_CONTROL (also known as “power control”, “Pwr_control”, “Pwr_ctrl”, or “P_ctl”) signal driven to the drive to control 5V and 12V power switches located on the drive. When this signal is asserted, high, 5V and 12V supplies are applied to the drive circuitry. When this signal is negated, low, 5V and 12V supplies are not connected to the drive circuitry, so that the drive circuitry is powered down. As described in SFF-8045, the drive provides a 10 KOhm pull up resistor from this signal to the 5V input to the drive.